1. Technical Field
This disclosure relates to odor reduction or elimination from air through the use of vapor phase hydrogen peroxide in combination with a media coated with a transition metal element or compound. Odor reduction or elimination is accomplished by the synergistic introduction of vapor phase hydrogen peroxide (VPHP) into malodorous air and allowing the malodorant and VPHP to engage a catalyst, where the catalyst comprises at least one transition metal element or compound.
2. Description of Related Art
The issue of malodors, and their potential adverse effects on health and quality of indoor life, has been a concern for centuries. While malodors are sometimes an indicator of danger or disease, they are typically little more than an unpleasant experience that negatively affect ambiance. Thus, for both nuisance and health reasons, methods have been sought to eliminate or substantially alleviate malodors wherever they are encountered, especially from indoor environments.
Many devices and techniques have evolved to treat malodors. Such methods or techniques have included masking odors with perfumes, fragrances or incense, displacing malodorous air with fans or blowers, absorbing malodors with activated carbon or other materials, and removing malodors from air using electrostatic precipitators. These methods and devices, though somewhat effective in lessening the impact of malodors, generally do not actually eliminate the malodorous substances themselves from the indoor environment.
While displacing malodorous indoor air with fans or blowers, and replacing it with fresh outdoor air may actually eliminate malodors from an indoor environment, such an approach to indoor malodor abatement is economically impractical when said indoor air is temperature and/or humidity controlled. Further, many indoor spaces such as high-rise apartments and high-rise offices do not have direct access to fresh outdoor air.
In the case of activated carbon, malodorous materials are not changed and may in fact be desorbed as a result of temperature fluctuations or interior carbon particle saturation—thus rendering this method less than optimally effective. The mechanism involved entails three separate (physical) processes which leave the malodorous substances intact: condensation, Van der Waals attraction and diffusion to the carbon particle interior.
Similarly, electrostatic precipitation consists essentially of a flocculation and subsequent collection of charged dust particles. Odor removal with this technique requires adsorption of malodors onto the targeted dust particles. Like techniques using activated carbon, this approach is clearly limited by the volatility and adsorbing propensity of the molecules involved. In any case, the odoriferous materials are not converted to less offensive compounds.
Perfume masking techniques (fragranced sprays, incenses, etc.) also leave the offending substances unchanged, which is less desirable than destroying, altering or deactivating the malodorous compounds. However, other approaches utilize chemical conversion to render malodorants innocuous. Examples of chemical conversion techniques include the use of promoters such as water-soluble ethylene oxide or propylene oxide derivatives, or mixtures of thereof. Other examples include molecules with one or more functional groups acting as a Lewis acid, Lewis base, oxidizing agent, reducing agent, or other functional group that will chemically neutralize the malodorant particles.
Finally, other techniques utilize materials that remove the malodorants from the gas phase and therefore reduce their partial pressure in the ambient air. For example, triethylene glycol, film forming polymers and cyclodextrins have been used to reduce the partial pressure of malodorants by physically removing malodor molecules from the ambient air without chemically neutralizing or altering them. In the case of triethylene glycol, the malodor molecules are partitioned into globules or droplets; in the case of film forming polymers, the malodors are “blanketed” or trapped; in the case of cyclodextrins, the malodors are trapped in the cage-like structure of cyclodextrins. In these scenarios, the malodors molecules are displaced rather than being chemically transformed into one or more less malodorous substances.
Hydrogen peroxide, an inexpensive and somewhat reactive oxidant, can also be used for malodor elimination or reduction by oxidizing malodorant molecules. However, current uses of hydrogen peroxide are limited to the use of aqueous solutions. For example, aqueous hydrogen peroxide solutions are used to remove food and smoke odors from the restaurant broiling grill emissions, in part through scrubbing of the grill exhaust gas stream through an aqueous peroxide solution. To be effective, the food must be cooked over thin, high temperature ceramic briquettes to enhance incineration of potential malodors, as well as scrubbing the grill gas stream with an aqueous hydrogen peroxide solution, followed by mixing the treated gas with ambient air prior to discharge to the atmosphere. Obviously, these systems are complex and costly and are not suitable for use by general consumers desiring to treat the air in an enclosed space.
Malodorous air may also be washed with an aqueous solution containing both hydrogen peroxide and ozone. For example, deodorization processes are known which generate and discharge ozone in combination with an atomized hydrogen peroxide solution. A reaction between ozone and atomized hydrogen peroxide generates a hydroxyl radical which is said to decompose various malodorous substances present in an indoor environment. However, the ozone generating requirement of these apparatuses makes them costly and potentially hazardous.
In a sewage treatment process, odor abatement is achieved by contacting hydrophobic components of an odor-containing gas plume condensate with odor-trapping core particles containing precipitates resulting from reaction ferrous ion, tannic acid, and hydrogen peroxide. Other processes utilize aqueous deodorant compositions containing hydrogen peroxide and nitrate ion or hydrogen peroxide, nitrate ion, and a transition metal salt. The aqueous deodorant compositions are typically mixed directly with the waste stream. Sulfide odors can be reduced or eliminated from the vapor spaces of waste handling and treatment systems by injecting a fine spray, mist or fog of an aqueous alkaline hydrogen peroxide solution into air spaces within sewage-containing system handling or treatment equipment.
Aqueous alkaline phosphate-containing hydrogen peroxide compositions for various odor elimination and disinfection uses are also known. The aqueous compositions are introduced onto surfaces and into air handling ducts by the application of a spray or mist of the aqueous alkaline peroxide solutions. The alkaline phosphate salts are said to enhance the oxidizing power of the peroxide and also to function as a peroxide stabilizer.
One catalytic process for removal of malodors from industrial gas streams includes scrubbing the gas stream through a fixed bed scrubber fitted with a solid packing bed containing a transition metal catalyst and hydrogen peroxide-containing liquor. While this technique is suitable for industrial systems, it is not applicable to home or office use.
Therefore, a need exists for malodor treatment compositions and methods which are straightforward and inexpensive to manufacture and which provide effective reduction or elimination of malodors in indoor air spaces and that can be safely used by the consuming public.